1. Field of the Invention
The present invention relates to a stimulable phosphor sheet employable in a radiation image recording and reproducing method utilizing a stimulable phosphor, and a method of conveying the stimulable phosphor sheet.
2. Description of Prior Arts
For obtaining a radiation image, there has been conventionally employed a radiography utilizing a combination of a radiographic film having a sensitive silver salt material layer and an intensifying screen.
As a method replacing the above-mentioned conventional radiography, a radiation image recording and reproducing method utilizing a stimulable phosphor as described, for instance, in U.S. Pat. No. 4,239,968, has been developed and paid much attention. The method involves steps of causing a stimulable phosphor to absorb a radiation having passed through an object or having radiated from an object; sequentially exciting (or scanning) the phosphor with an electromagnetic wave such as visible light or infrared rays (i.e., stimulating rays) to release the radiation energy stored in the phosphor as light emission (i.e., stimulated emission); photoelectrically detecting the emitted light to obtain electric signals; and reproducing the radiation image of the object as a visible image, numerals, symbols, etc. from the electric signals.
In the radiation image recording and reproducing method, a radiation image is obtainable with a sufficient amount of information by applying a radiation to the object at a considerably smaller dose, as compared with the conventional radiography. Accordingly, the radiation image recording and reproducing method is of great value, especially when the method is used for medical diagnosis.
In performing the radiation image recording and reproducing method, a stimulable phosphor is generally employed in the form of a stimulable phosphor sheet (also referred to as a radiation image storage panel, and generally in the form of a sheet of rectangle, square, etc.) which comprises a support and a phosphor layer provided thereon. The phosphor layer comprises a stimulable phosphor and a binder. Further, a protective film made of a transparent plastic film is provided on the surface of the phosphor layer to protect the phosphor layer from physical and chemical deterioration.
The stimulable phosphor sheet does not serve to finally record image information, but only stores the information temporarily to provide the image or the like on an independently prepared final recording medium as described above. Accordingly, the stimulable phosphor sheet can be repeatedly used and such repeated use brings about economical advantage.
The repeated use of the stimulable phosphor sheet is particularly advantageous, for instance, in the case that a radiation image information recording and reading device employing the stimulable phosphor sheet is mounted on a traveling station such as a radiographic apparatus-carrying car to conduct mass radiographic examination in various places. More in detail, it is inconvenient to carry a great number of stimulable phosphor sheets on a traveling station, and there is a limitation on the number of sheets capable of being carried on a car such as a radiographic apparatus-carrying car. Accordingly, it is practically useful that the stimulable phosphor sheets are mounted on a radiographic car under such conditions that the stimulable phosphor sheets are repeatedly used; radiation image information of an object is recorded on each stimulable phosphor sheet and read out to obtain image information as a signal; and the obtained signal is transferred to a recording medium having a great recording capacity such as a magnetic tape so as to repeatedly use the stimulable phosphor sheet in cycle. This means that radiation images of a number of objects can be obtained by the use of a small number of stimulable phosphor sheets. Further, the combination of the repeated use of the stimulable phosphor sheets with a continuous radiographic process enables to perform rapid radiography in the mass radiographic examinations. This combination is of great value in practical use.
In the case of using the stimulable phosphor sheets repeatedly in cycle, after the radiation energy stored in the stimulable phosphor sheet is read out and aimed image information is obtained, the remaining energy in the sheet is released and erased in a manner as disclosed, for instance, in Japanese Patent Provisional Publication Nos. 56(1981)-11392 and 56(1981)-12599. By employing such manner, the stimulable phosphor sheet can be efficiently and repeatedly used in cycle.
Thus, the radiation image information recording and reading device, in one aspect, is desirably mounted on a traveling station such as a radiographic apparatus-carrying car in the form of a united built-in device which comprises an image recording means for exposing a stimulable phosphor sheet to a radiation having passed through an object so as to record and store a radiation image in the stimulable phosphor sheet, a read-out means for reading out the radiation image stored in the stimulable phosphor sheet, an erasure means for releasing and erasing radiation energy remaining in the stimulable phosphor sheet for the next use of the stimulable phosphor sheet, and a conveyance means for moving the stimulable phosphor sheet in cycle to each of the above-mentioned means. The radiation image information recording and reading device having the above-mentioned constitution have various advantages not only in its installation in the traveling station such as a radiographic apparatus-carrying car but also in setting in hospitals, so that the above device is convenient in practical use.
The radiation image information recording and reading device utilizing the above-mentioned system of repeatedly and cyclically using the stimulable phosphor sheet is disclosed in U.S. patent application Ser. No. 600,689 filed in the name of the present assignee. In the device, the stimulable phosphor sheet is occasionally conveyed vertically or almost vertically for the purpose of making the device compact.
If a stimulable phosphor sheet suffers physical deterioration such as a scratch on the surface of the protective film, the quality of image or the accuracy of image information provided by the phosphor sheet tends to decrease markedly. For this reason, it is necessary to select the means for conveying a stimulable phosphor sheet with such a careful consideration that the surface of the stimulable phosphor sheet should not be damaged. From this viewpoint, as a means for conveying a stimulable phosphor sheet, a belt conveyor made of a soft sheet-material is generally employed. However, while the belt conveyor is suitable for conveying the stimulable phosphor sheet horizontally, it is unsuitable for conveying the stimulable phosphor sheet in the direction other than the horizontal direction, particularly in the vertical or almost vertical direction. More in detail, in the process for conveying a stimulable phosphor sheet vertically or almost vertically using a belt conveyor, it is necessary to arrange a pair of belt conveyors in such a manner that the belt conveyors are in face to face contact with each other so as to convey the stimulable phosphor sheet under the condition that the stimulable phosphor sheet is sandwiched between that pair of belt conveyors. However, said conveying device is complicated in structure, and it is difficult to make the device compact. Further, there are other problems such that the surface of the stimulable phosphor sheet tends to suffer scratches when the rate of one belt conveyor is made different from that of the other, even if the difference therebetween is very small.